What are you using to measure, and is it set to db A or C?18db is very quiet - you would need a special device to measure that low. A smartphone will not be accurate.
On another related note, how much background noise does your system add? In other words, what’s the noise level with your system off, vs on? I measure +0.5-1dB with it on. 35dB off -> 35.5/36dB on. Is that good?
I sit 10’ away from 105dB sensitive horns, but have a new crossover on the way which should reduce it further.